1. Technical Field
This invention relates to digital image display systems and, more particularly, to a method and apparatus for compiling digital image information for display.
2. Description of the Prior Art
With the advent of viewdata and teletext services, a number of independently developed systems for generating digital data for display have surfaced. Stafford et al., U.S. Pat. No. 4,240,140 discloses one such system comprising CRT display terminal priority interrupt apparatus for generating vectored addresses. The Stafford system comprises a bidirectional data bus and an address bus so that video data processing subsystems are able to intercommunicate, their activities being governed by a clock and interrupt system.
Two problems remain largely unsolved in such systems. One has become known as the hidden line problem. This has been described as the problem of determining which edges of a solid, nontransparent object are visible (and which invisible) from a given vantage point. A brief history of the problem is presented in H. Freeman's, "Interactive Computer Graphics," at pages 201-202. Stated another way, it is desirable in display systems to allow a first solid object to appear to cover a second solid object; the second solid object, a third, and so on. Proposed solutions to this problem generally involve the development of complex algorithms which require considerable processor time. Roe et al., U.S. Pat. No. 4,217,577 and Johnson, U.S. Pat. No. 4,222,048 exemplify such state of the art solutions.
The time consumed in processing complex algorithms for solving the hidden line problem precludes solution of the second problem which is to provide animation in digital image display systems. The animation problem overlaps with the hidden line problem and comprises the following subset of problems: size enlargement (zooming), movement, and rotation of a solid object. These are desirable characteristics of an animated computer display system, but, as yet, practical solutions to the animation problem are not available.
Freeman, at page 331, presents a brief history of the animation problem. He suggests that present solutions to the problem include the development of sophisticated animation languages which, to a degree, increase the speed of algorithm processing. Animation processors perform complex transformations on the three dimensional surfaces of solid objects.
It is clear, however, that there remains a requirement for a viable alternative solution to the problems of the hidden line and animation. It is also desirable that such a system compliment presently suggested solutions.